Optical shutters are typically designed to operate at high speeds, switching between fully open and fully closed positions at rates that can be as high as several times per second for some types of optical equipment. To provide this type of highly repetitive operation, optical shutter designs are generally lightweight and are often mechanically complex.
One characteristic problem of high speed shutter systems is aptly termed “bounce”, an undesirable shutter rebound behavior that tends to extend the effective opening and closing transition times of the shutter. To correct this problem in operation at high speeds, the shutter apparatus typically requires some type of damping mechanism. Effective damping helps to improve performance and to eliminate perceptible bounce or related transient effects. In addition, by softly slowing the movement of the shutter components near the end of their movement path and without damage, damping helps to prolong the effective lifetime of a shutter system, reducing the effect of repetitive impact and consequent wear on the shutter blades and drive components. Damping mechanisms can be used for shutter systems with a single shutter blade or for multi-shutter systems having any number of shutter blades.
Some types of optical shutter have multiple shutter blades that are pivotally mounted about an aperture. In rotary shutters of this type, each blade pivots inwards to block its portion of the aperture, and pivots outwards to open the aperture. To synchronize operation of the plurality of blades, the drive mechanics for each blade are coupled to a rotatable drive ring that orbits the aperture. Rotation of this rotatable drive ring over a small arc in one direction synchronously causes the blades to swing in unison to an open position, opening the aperture. Rotation in the opposite direction causes the blades to swing together to a closed position over the aperture. Conventional shutter solutions use a solenoid to drive the rotatable drive ring to the first and second positions that open or close the shutter. It has been found, however, that high force transmission from a single solenoid can cause high levels of wear on the ring and associated linkage components.
A number of damping solutions have been developed and used for rotatable ring and various other types of shutter. One type of conventional solution uses bumpers of polyurethane or other plastic material, implemented as part of a complex arrangement of springs and resilient members for damping the rotatable drive ring. Other shutter designs have used various types of resilient materials arranged to directly absorb the impact of shutter blades or of the drive linkages themselves.
There are a number of problems with conventional damping solutions, particularly for optical shutters that use a rotatable drive ring for blade synchronization. Bumper materials age over time and can be reshaped or experience uneven wear due to continuing, repetitive impact. After repeated use, some unwanted sticking can occur at the bumper interface. Springs and other components under tension exhibit wear and their coercive properties can change with repeated use. Complex solutions that counter these problems can be costly to design and implement and durability can be compromised.
Thus, it can be seen that there is a need for a damping arrangement that is straightforward to implement, low-cost, high in performance, and particularly well suited for use with optical shutters that use a rotatable drive ring for multiple blade synchronization.